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Old 8th June 2011, 07:03 PM   #111
effebi is offline effebi  Italy
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Quote:
Originally Posted by wahab View Post
Well, the output stage would still use the same components
while TMC would require adding a little cap and a resistor.

Hardly a big change in the topology..
I also believe that P3A will sound differently with a standard (boring) EF.
The crossover behaiviour should be completely different, at least if low- biased at 30-50. The graphs and measures on D. Self book are very esplicative on that subject.

Then
I have read here in similar amplifiers threads that (OS's BX ?, JAS ?) that TMC won't work without a high open loop gain (say 120 dB). I do not believe that P3A has so much. But I am not expert on this more "refined" compensation to say more.
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Old 8th June 2011, 07:26 PM   #112
wahab is offline wahab  Algeria
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Quote:
Originally Posted by effebi View Post
I also believe that P3A will sound differently with a standard (boring) EF.
The crossover behaiviour should be completely different, at least if low- biased at 30-50. The graphs and measures on D. Self book are very esplicative on that subject.
Boring??...
An EF , according to Self s measures produce significantly
less distorsion at low levels.
Besides, he use very old slow devices in theses measurement.
Would you use MJ802/MJ4502 pair in a modern design unless
it is for a bass box ?..

Quote:
Originally Posted by effebi View Post

Then
I have read here in similar amplifiers threads that (OS's BX ?, JAS ?) that TMC won't work without a high open loop gain (say 120 dB). I do not believe that P3A has so much. But I am not expert on this more "refined" compensation to say more.
effebi
To the contrary, TMC works better with high OLG amps provided
the VAS has very high gain.
Of course , it works not as well in amps such as P3A but it bring
significant improvement that is worth taking account of since
this amp s VAS has a gain on the order of 60db.
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Old 8th June 2011, 08:55 PM   #113
effebi is offline effebi  Italy
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Quote:
Originally Posted by wahab View Post
Boring??...
An EF , according to Self s measures produce significantly
less distorsion at low levels.
Besides, he use very old slow devices in theses measurement.
Would you use MJ802/MJ4502 pair in a modern design unless
it is for a bass box ?..


To the contrary, TMC works better with high OLG amps provided
the VAS has very high gain.
Of course , it works not as well in amps such as P3A but it bring
significant improvement that is worth taking account of since
this amp s VAS has a gain on the order of 60db.
Yes, boring, very boring . When something is used by everybody becomes boring. I am not saying it is not good or that has not some adavantages. Just (highly subjectively)boring.

I am sure to remeber that Self (on the 3rd ed. I believe) demonstrates that as OP stage CFP has LESS (CROSSOVER) distorsion, with numbers and graphics.

Many CFP also work well with "relatively" modern devices like the ones quoted by Sakis (or the omni present 2500/1943), so I do not see your point so easily criticizing the Self's choice. Maybe I am misunderstanding you, sorry for that.
BTW I have around a PA3 with (slow!) 15003/4 OP that sounds very good (to some people with good ears, not mine) but I do not have instrumental THD measuments to support my thesis, so it's up to you . And no, it is not for a bass box and yes is HF stable with TO3 mounted on the same PCB.

About the TMC , seems we agree that the OLG should be high, just some members here had experimentally quite bad results with smaller numbers than 120. I agree also that the tecnique should bring neat improvements, if made to work. I would give it a try as soon I have P3A on hand again, I am courious now.
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Old 8th June 2011, 09:38 PM   #114
wahab is offline wahab  Algeria
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Quote:
Originally Posted by effebi View Post
I am sure to remeber that Self (on the 3rd ed. I believe) demonstrates that as OP stage CFP has LESS (CROSSOVER) distorsion, with numbers and graphics.


About the TMC , seems we agree that the OLG should be high, just some members here had experimentally quite bad results with smaller numbers than 120. I agree also that the tecnique should bring neat improvements, if made to work. I would give it a try as soon I have P3A on hand again, I am courious now.
effebi
Quote:
though it is noticeable that the EF gives a good deal less distortion at lower power levels around 1 W. This is an unexpected observation, and is probably due to the greater width of the EF crossover region.
Distortion In Power Amplifiers

P3A works better , in sims at least, with EF than CP.
TMC will not improve a CP version by much but in conjunction
with an EF OS , it will improve the THD ratios by some margins,
although the result will surely be unoticeable in listening tests,
but who knows..
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Old 8th June 2011, 10:34 PM   #115
effebi is offline effebi  Italy
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I know the article. However, for what I could understad, the explanation of the phenomena is "unexpected". What is well documented is the different linearity of the two stages ( being the CFP about 1/4 deviation, although more concetrated), if you look at the graphics.
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Old 8th June 2011, 10:42 PM   #116
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Personally i cant hear any difference between EF and CF, and i think EF is more popular because its less susceptible to oscillation than CF.
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Old 8th June 2011, 11:01 PM   #117
wahab is offline wahab  Algeria
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Quote:
Originally Posted by effebi View Post
I know the article. However, for what I could understad, the explanation of the phenomena is "unexpected". What is well documented is the different linearity of the two stages ( being the CFP about 1/4 deviation, although more concetrated), if you look at the graphics.
Funny that i elected to use the ones on the third curve ,
2SJ50/2SK135 as definitive devices in almost all the amps
i built since late 80s...

Indeed, they allow very good stability and very wide OLG.

As pointed by Tekko, CFP are less stable when used in amps
that have global NFB , and this show in simulations by wider
bandwith of THD residuals.
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File Type: gif ESP P3A CP VS EF.gif (38.3 KB, 574 views)
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Old 9th June 2011, 11:14 AM   #118
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one thing i havent try but would like to, is a combination of fast drivers but with slower output ...something like good quality MJ 15003-4

Thing is that if i do that obviously have to make a new pcb to accomodate the above properly ...will see
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Old 9th June 2011, 12:25 PM   #119
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Hi Sakis
MJ15003/4 are Ft 2 MHz and MJL21193/4 only a little higher at 4 MHz.
They are easy to swap, so maybe worth the effort of testing?
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Old 9th June 2011, 12:37 PM   #120
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dont know ian ....willing to find out though ....
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